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Synthesis of trans-Cycloalkenes via Enantioselective Cyclopropanation and Skeletal Rearrangement Tomoya Miura, Takayuki Nakamuro, Chia-Jung Liang, and Masahiro Murakami J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja5096045 • Publication Date (Web): 22 Oct 2014 Downloaded from http://pubs.acs.org on October 28, 2014
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Synthesis of trans-Cycloalkenes via Enantioselective Cyclopropanation and Skeletal Rearrangement Tomoya Miura,* Takayuki Nakamuro, Chia-Jung Liang,† Masahiro Murakami* Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan Supporting Information Placeholder N-sulfonyl-1,2,3-triazoles.11 Our previous study12 on the reacABSTRACT: An efficient one-pot two-step procedure for tion of spiropentanes led us to examine the use of methyleneasymmetric synthesis of piperidine-fused trans-cycloalkenes is cyclopropanes, hoping that enantioenriched spiropentanes bereported. The method comprises the initial enantioselective came accessible.13,14 Thus, we treated methylenecyclopropane installation of another cyclopropane ring onto methylenecy2a (1.5 equiv), which was synthesized from cis-cyclooctene clopropanes and the subsequent thermal skeletal rearrangement simply according to a literature procedure,15 with 1-mesyl-4in which the installed as well as inherent cyclopropane rings phenyl-1,2,3-triazole (1a, 1.0 equiv) in the presence of (tBuare both opened. A concerted mechanism is proposed for the CO2)4Rh2 (1.0 mol %) and 4 Å molecular sieves (MS) in latter thermal rearrangement reaction together with a closed CHCl3 (0.2 M) at 40 °C (eq 1). The cyclopropanation reaction transition state model. was complete in 5 h, and after chromatographic purification, α-imino spiropentane 3a was obtained as a single diastereomer Both cis and trans isomers are synthetically accessible for in 85% yield. The stereochemistry is explained by assuming cyclic alkenes consisting of more than 7 carbon atoms. Unlike that the carbenoid species has added onto the exocyclic C–C acyclic alkenes, trans isomers of cyclic alkenes from seven- to double bond of 2a from its less-hindered side. ten-membered ring are less stable than their cis counterparts.1 Ms (tBuCO 2)4Rh 2 Ms Seven-membered trans-cycloheptene is too distorted to retain N (1.0 mol %) 2 N H its trans geometry at temperatures higher than –78 °C. The (1) 8 + N CHCl 3, MS torsion strain is alleviated by increment of the ring-size, and 8 N Ph Ph 40 °C, 5 h eight-membered trans-cyclooctene is stable at room tempera2a (1.5 equiv) 1a 3a 85% ture. Medium-sized cyclic trans-alkenes take twisted forms, 16 and are characterized by planar chirality. The properties inherNext, the thermal reactivities of 3a were investigated, and ent to their unique structures have found a wide variety of apan unprecedented rearrangement reaction was identified; when 3 4 plications in organic synthesis and chemical biology. There3a in CHCl3 (0.2 M) was heated at 120 °C under microwave fore, the development of stereoselective preparative methods irradiation (MW) in a sealed microwave vial for 2 h, the piperof medium-sized cyclic trans-alkenes has been a subject of idine-fused cyclononene 4a was cleanly formed in a stereo5 considerable investigation. Yet, synthetic methods available chemically pure form (85% isolated yield), and its nOe study for optically active ones are limited. There are only a few exin 1H-NMR proved the trans geometry for its bridgehead dou6 amples of enantioselective syntheses, and the other precedents ble bond (eq 2). The C(1)–C(1’) σ-bond, C(2’)–C(3’) σ-bond, are based on either resolution of racemates7 or multi-step deriand C(2)–N(3) π-bond of 3a are cleaved, and instead the N(3)– 8 vatization of chiral pool molecules. Now, we report a one-pot C(3’) σ-bond, C(1)–C(2) π-bond, and C(1’)–C(2’) π-bond are two-step procedure for the synthesis of enantioenriched piperinewly formed with 4a with installation of a trans geometry for dine-fused trans-cycloalkenes from achiral methylenecyclothe C(1’)–C(2’) double bond. These bond cleavages and forpropanes and triazoles. The procedure can be modified even to mations result in a structural reorganization of the tricyclic directly start from terminal alkynes in place of triazoles (Figskeleton into the twisted bicyclic skeleton. ure 1). Ms
R + MsN 3 +
cat. cat. CuI RhII n
Ms N H
∆
H
n
R
Ms N *
N3 H n
R
Figure 1. Construction of piperidine-fused trans-cycloalkenes from terminal alkynes, mesyl azide, and methylenecyclopropanes.
N-Sulfonyl-1,2,3-triazoles are readily prepared from terminal alkynes and N-sulfonyl azides using copper(I) catalyst.9 Upon treatment with rhodium(II) or nickel(0) complexes, they generate metal complexes of α-imino carbenes, which subsequently react with various electron-rich compounds.10 Fokin and co-workers reported a rhodium(II)-catalyzed, highly enantioselective cyclopropanation reaction of simple alkenes with
2
1
H
2
Ms 3 N 3' 9
3' 1'
Ph
8 2'
3a
CHCl 3, 120 °C/MW, 2 h
Ph
1
1'
(2)
2'
4a 85%
This thermal rearrangement reaction is generalized as depicted in Figure 2. If we focus on the cleavage of the C(1)– C(1’) σ-bond occurring with A and the formation of the N(3)– C(3’) σ-bond occurring with B, the former σ-bond migrates to the new position between the N(3) and C(3’) atoms which are both two atoms removed from the bonded loci. In this sense, the present skeletal rearrangement can be described as a [3,3] sigmatropic rearrangement. In the case of the retro process17 of the Claisen rearrangement from C to D, which would serve as a prototype for [3,3] sigmatropic rearrangement, the C(1)– C(1’) σ-bond being cleaved with C is flanked by two
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2
3
1
N
1'
3
1
3'
2'
N 3'
1'
A
(retro-Claisen rearrangement) 2
2
1
O3
1
1'
3'
1'
B
2'
2
O3 3'
2'
2'
C
D
Figure 2. The general diagram of thermal rearrangement.
π-electron systems. Terminal sp2 atoms [O(3) and C(3’)] change into sp3 atoms by losing a π-bond and gaining a new σbond between themselves. The structural deviation of A from C is that a cyclopropane ring replaces one π-electron system of C. With A, the σ-bond being cleaved is flanked by one πelectron system and one cyclopropane ring. The sp3 C(3’) loses the σ-bond to C(2’) gaining a new σ-bond to N(3). The major driving force of the present skeletal rearrangement is presumably attributed to the release of the ring strain of the spirocyclic structure (ca. 61 kcal/mol), which is considerably larger than the double of the ring strain of a simple cyclopropane ring (ca. 28 kcal/mol).18 The transition state model F is proposed for the skeletal rearrangement of 3a in analogy with that of the retro process of the Claisen rearrangement reaction (Scheme 1).17 The sigmatropic interconversion between γ,δ-unsaturated aldehydes and allyl vinyl ethers is assumed to proceed via a closed six-membered chair-like transition state model E. The α-imino spiropentane 3a can be considered as the cyclopropane homolog of γ,δunsaturated aldehydes, and therefore, the transition state model F which is conformationally analogous to E can be expected on the mechanistic pathway from 3a to 4a. The transition state model F reasonably depicts how the stereochemistry at the C(2’) position dictates the geometry of the resulting bridgehead double bond. The substituent at C(2’) orients downward in parallel to the methylene bridge of the adjacent cyclopropane ring, and upon skeletal rearrangement, the π-bond develops in between with these orientations retained. Further support was lent to the transition state model F by additional experimental results (vide infra). Scheme 1. The Proposed Transition State Model (retro-Claisen rearrangement)
R1
3
2 1
3
2
3'
O 1'
2'
3'
O
R2
1
R3
1' 2'
E
(this work)
Ms 2 1
Ph
3
N
H
3'
1' 2'
3a
Ms H
2
3
N 1
Ph
3'
1' 2'
F
[(S)-NTTL]4Rh 2 (2.5 mol %)
1a + 2a (1.5 equiv) CHCl 3, MS 40 °C, 8 h
3
2
O 1
R3
1' 2'
‡ 2
H
1
Ph
3'
Ms N
(1.0 equiv)
(3)
Ph
4a CH2Cl2 rt, 13 d
Cl N
Pt Cl
5 80%
The two-step transformation of 1a and 2a into the enantioenriched 4a was successfully integrated into a one-pot procedure (Table 1).21 The trans-cyclononene 4a was prepared in 88% yield with 97% ee by applying the two reaction conditions to the mixture of 1a and 2a in sequence (entry 1). Various other 4-aryl-substituted triazoles 1b–e were subjected to the one-pot procedure, and similar results were obtained when a mixed solvent of chloroform/methanol was used; trans-cyclononenes 4b–e were produced in good yield with enantioselectivities ranging from 93% ee to 98% ee (entries 2–5). 4-(1Cyclohexenyl)triazole 1f was also a suitable triazole (entry 6). On the other hand, a complex mixture arose from alkylsubstituted triazoles, because the latter thermal skeletal process was more sluggish. Table 1. One-Pot Transformation of Triazoles 1 and 2aa 1) [(S)-NTTL]4Rh 2 (2.5 mol %)
Ms N
R2 R3
Ms 3 H3' nOe H N
CHCl 3, MS, 40 °C, 8 h
N+
N 1
2) CHCl 3, 120 °C/MW, 2 h
Ms N
R1
2a (1.5 equiv)
4
yield (%) b ee (%)
entry
1
R1
4
1
1a
Ph
4a
88
97 98
2
1b
4-MeO-C6H 4
4b
82c
3
1c
4-CF3-C6H 4
4c
91c
97 96
4
1' 2'
4a
Thus, the piperidine-fused trans-cyclononene 4a was stereoselectively constructed from 2a through the cyclopropanation with 1a and subsequent thermal skeletal rearrangement. Next, we challenged the asymmetric synthesis of 4a by using chiral rhodium(II) catalysts in the first cyclopropanation reaction. As with the case of cyclopropanation of simple alkenes,11 an excellent enantioselectivity of 96% ee was observed with 3a when [(S)-NTTL]4Rh2 (2.5 mol %, NTTL = N-naphthoyl-tertleucinate) was used as the catalyst (eq 3). Of note was that three new chiral centers were stereoselectively installed in a single step. Then, the enantioenriched spiropentane 3a was subjected to the second skeletal rearrangement reaction. The resulting trans-cyclononene 4a exhibited an enantiopurity of
3a 4a CHCl 3 86% 83% (97% ee) 120 °C/MW (96% ee) 2h
Cl N Pt Cl
R1
R2
H
97% ee to assure the integrity of chirality transfer within an experimental accuracy during the skeletal rearrangement. In order to determine the absolute stereochemistry of 4a, we followed a procedure in literature19 to treat it with transPtCl2(2,4,6-collidine)(η2-ethylene). The resulting platinum(II) complex 5 was obtained as a crystalline solid and its singlecrystal X-ray analysis proved the absolute stereochemistry.20
R1
‡
R1
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1d
2-naphthyl
4d
88c
5
1e
3-thienyl
4e
93c
93
6
1f
1-cyclohexenyl
4f
83
98
a
A 0.2 mmol scale. bYield of isolated product (average of two runs). cThe second step [CHCl3/MeOH (1/1), 100 °C/MW, 3 h].
Exemplified in Scheme 2 is an ultimate one-pot procedure starting directly from terminal alkynes. An arylethyne, mesyl azide, 2a, CuTC, [(S)-NTTL]4Rh2, MS, and CHCl3 were all placed in a reaction vessel, and the reaction mixture was stirred from 0 °C to 25 °C for 10–16 h, and subsequently at 100 °C under MW irradiation for additional 3 h. Finally, the cooled reaction mixture was subjected to chromatographic purification. The products 4a, 4b, and 4f were isolated in 60–67 % overall yields with excellent enantioselectivities (97–99% ee)
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according to this all-in-one-pot procedure. It is notable that the molecular complexities including the absolute stereochemistry have dramatically increased through this one-pot process, during which a work-up procedure is executed only once. Scheme 2. One-Pot Synthesis Starting from Terminal Alkynes 1) 10 mol % CuTC 2.5 mol % [(S)-NTTL]4Rh 2 CHCl 3, MS, 0 °C–rt, 10–16 h
R1
+ MsN 3
+
2) CHCl 3/MeOH (1/1)
2a (1.5 equiv)
100 °C/MW, 3 h
Ms N
nPr
R1
R1 = Ph R1 = 4-MeO-C6H 4 R1 = 1-cyclohexenyl
oriented away from the other propyl group (eq 7). The first cyclopropanation reaction would have occurred selectively from the less-hindered side of 2c to form the intermediary spiropentane 3c diastereoselectively as with the case of 2a. Granting this stereoselectivity, the double bond stereochemistry of 6 is in accordance with the proposed transition state model I with the two propyl groups oriented downward, one is in a pseudoaxial position and the other is in a pseudoequatorial position, which is also virtually similar to the model F.
1a
2) CHCl 3, 120 °C/MW, 2 h
Ms N
1a + nPr
(rac) 2b (1.5 equiv)
CHCl 3, MS 40 °C, 4 h
Ms N
nPr
+
Ph
nPr
3b1 67% NMR
Ph
nPr
(4) nPr
3b2 26% NMR
The subsequent skeletal rearrangement of the major diastereomer 3b1 under the standard thermal conditions (120 °C/MW) was slower than that of 3a to afford piperidine derivative 6 in 44% yield after 14 h (eq 5). Noteworthy was the exclusive stereochemistry of the exocyclic double bond; the propyl substituent is oriented away from the other propyl group. In contrast, the rearrangement of the minor diastereomer 3b2 was much faster than that of 3b1 to selectively produce the geometrical isomer 7 with its propyl substituent oriented in the opposite direction in 85% yield (eq 6). The stereospecificity observed with the reaction using the pair of the diastereomers 3b1 and 3b2 is well accounted for by assuming the transition state models G and H, which are similar to the model F in Scheme 1. Moreover, the transition state models G and H explain the slower reaction of 3b1; the transition state model G having the two propyl substituents in pseudoaxial positions would be energetically higher than H having the two propyl substituents in pseudoequatorial positions. Ms N Ph 3b1
Ms N Ph 3b2
nPr
CHCl 3 nPr 120 °C/MW 14 h nPr
nPr
Ms N Ph
(5)
n 6 44% Pr
Ph
nPr nPr
H H
Ms N
‡
H
H
Ph
nPr
G Ms
nPr
HH
N CHCl 3 nPr 120 °C/MW 14 h
Ms N
‡
nPr
(6)
nPr
Ph 7 85% H
On the other hand, the one-pot, two-step transformation of 2c, prepared from cis-oct-4-ene, using 1a and (tBuCO2)4Rh2 yielded the piperidine derivative 6 with the propyl substituent
nPr
nPr
3c
(7)
Ms N
‡
H
Ms
In order to corroborate the transition state model F proposed above, the two-step transformation was examined in more detail using a pair of symmetrically disubstituted methylenecyclopropanes 2b and 2c prepared from trans- and cis-oct-4-ene, respectively. The cyclopropanation reaction of the racemic 2b with the triazole 1a using (tBuCO2)4Rh2 as the catalyst yielded a 5:2 mixture of diastereomers 3b1 and 3b2 (eq 4). The diastereomers were separated by HPLC, and their structures were determined by a set of NMR analyses (DEPT, COSY, HMQC, HMBC, and nOe). (tBuCO 2)4Rh 2 (2.0 mol %)
Ph
2c (1.5 equiv) nPr
N
nPr
Ms N
CHCl 3, MS, 40 °C, 8 h
+ nPr
4a 67% (97% ee) 4b 60% (99% ee) 4f 63% (97% ee)
1) (tBuCO 2)4Rh 2 (1.0 mol %)
nPr
H
Ph
nPr
H
Ph
I
6 85%
nPr
Methylenecyclopropanes derived from cycloalkenes of other ring-sizes than eight were also employed in the sequential transformation. When 10-methylenebicyclo[7.1.0]decene (2d), derived from cis-cyclononene, was subjected to the cyclopropanation reaction with 1a using [(S)-NTTL]4Rh2 as the catalyst at 40 °C, the second skeletal rearrangement reaction occurred concurrently with the first cyclopropanation to directly furnish trans-cyclodecene 8 in 94% yield with 97% ee (eq 8). We suppose that the faster reaction may be ascribed to the conformation of the intermediate spiropentane derived from 2d; the intermediate spiropentane would be conformationally closer to the transition state of the skeletal rearrangement than in the case of 3a so that a smaller structural change is required to reach the transition state. N N Ph
+
9
N 1a
Ms N
[(S)-NTTL]4Rh 2 (2.5 mol %)
Ms
2d (1.5 equiv)
CHCl 3, MS 40 °C, 14 h
10
(8)
Ph 8 93% (97% ee)
The stability of planar chirality of medium-sized transcycloalkenes generally decreases with increment in ring size, and trans-cyclononene racemizes considerably faster (t1/2 = 6 s at 30 °C) than trans-cyclooctene (t1/2 = ~105 years at 30 °C) through swiveling of the twisted double bond.22 Nonetheless, double bond swiveling was not observed with both 4a and 8 up to 120 °C. We suppose that the twisted conformation is locked by the central chirality at the bridgehead position,8a which has been originally set in the achiral molecules upon the enantioselective cyclopropanation. On the other hand, the eight-membered trans-cyclooctene derivative 9 (eq 9) was expected to be more strained than the cyclononene and cyclodecene counterparts 4a and 8.1 We next tried to synthesize 9 by using 8-methylenebicyclo[5.1.0]octane (2e), derived from cis-cycloheptene. When the standard conditions of the one-pot two-step transformation (2.5 mol % of [(S)-NTTL]4Rh2 at 40 °C for 8 h, then at 120 °C/MW for 2 h) were applied to a mixture of 1a and 2e, the major product was the corresponding α-imino spiropentane because the second rearrangement reaction was considerably slower than that of 3a. Then, the duration of time of heating (120 °C/MW) for the second skeletal rearrangement was extended to 12 h, and a mixture of trans-cyclooctene 9 (18% NMR yield, 98% ee), ciscyclooctene 10 (40% NMR yield, 98% ee), and 1,3-diene 1123 (37% NMR yield, 6% ee) was generated. Although it was pos-
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sible to separate them by HPLC, a mixture of 9 and 10 (5:2)24 resulted again even when the purified trans-cyclooctene 9 was left in vacuo at room temperature for 9 h. Thus, decrease in ring size from nine to eight brought about a significant increase in the structural strain. Ms N N Ph
N
+
7 2e (1.5 equiv)
1a
1) [(S)-NTTL]4Rh 2, (2.5 mol %) CHCl 3, MS, 40 °C, 8 h 2) CHCl 3, 120 °C/MW, 12 h
(9) Ms N
Ms N 8
+
8
Ph
Ph
9 18% NMR (98% ee)
10 40% NMR (98% ee)
Ms N
+
8
Ph 11 37% NMR (6% ee)
In summary, we have developed a new method for the asymmetric synthesis of piperidine-fused trans-cycloalkenes, which comprises the enantioselective construction of a cyclopropane ring and the thermal skeletal rearrangement opening the two cyclopropane rings.
ASSOCIATED CONTENT Supporting Information. Experimental procedures, spectral data for the new compounds, and details of the X-ray analysis. This material is available free of charge via Internet at http://pubs.acs.org.
AUTHOR INFORMATION Corresponding Author
[email protected];
[email protected] Notes The authors declare no competing financial interest. † C.L. is on leave from Department of Chemistry, National Taiwan Normal University, Taipei, Republic of China.
ACKNOWLEDGMENT The paper is dedicated to Prof. A. B. Smith, III on the occasion of his 70th birthday. We thank Dr. Y. Nagata (Kyoto University) for kind help in an X-ray analysis and Prof. K. Tomooka and Dr. K. Igawa (Kyushu University) for useful advice. This work was supported in part by a Grant-in-Aid for Scientific Research (B) from MEXT and the ACT-C program of the JST.
REFERENCES (1) Barrows, S. E.; Eberlein, T. H. J. Chem. Educ. 2005, 82, 1334. (2) Squillacote, M. E.; DeFellipis, J.; Shu, Q. J. Am. Chem. Soc. 2005, 127, 15983 and references therein. (3) (a) Dorr, H.; Rawal, V. H. J. Am. Chem. Soc. 1999, 121, 10229. (b) Lledó, A.; Fuster, A.; Revés, M.; Verdaguer, X.; Riera, A. Chem. Commun. 2013, 49, 3055. (4) Selvaraj, R.; Fox, J. M. Curr. Opin. Chem. Biol. 2013, 17, 753 and references therein. (5) (a) Nakazaki, M.; Yamamoto, K.; Yanagi, J. J. Am. Chem. Soc. 1979, 101, 147. (b) Royzen, M.; Yap, G. P. A.; Fox, J. M. J. Am. Chem. Soc. 2008, 130, 3760. (c) Wang, X.-N.; Krenske, E. H.; Johnston, R. C.; Houk, K. N.; Hsung, R. P. J. Am. Chem. Soc. 2014, 136, 9802 and references therein. (6) (a) Deiters, A.; Mück-Lichtenfeld, C.; Fröhlich, R.; Hoppe, D. Chem. Eur. J. 2002, 8, 1833. (b) Tomooka, K.; Uehara,
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K.; Nishikawa, R.; Suzuki, M.; Igawa, K. J. Am. Chem. Soc. 2010, 132, 9232 and references therein. (7) (a) Tomooka, K.; Komine, N.; Fujiki, D.; Nakai, T.; Yanagitsuru, S. J. Am. Chem. Soc. 2005, 127, 12182. (b) Tomooka, K.; Suzuki, M.; Shimada, M.; Yanagitsuru, S.; Uehara, K. Org. Lett. 2006, 8, 963. (8) (a) Nakazaki, M.; Naemura, K.; Nakahara, S. J. Org. Chem. 1979, 44, 2438. (b) Sudau, A.; Münch, W.; Nubbemeyer, U.; Bats, J. W. J. Org. Chem. 2000, 65, 1710. (c) Larionov, O. V.; Corey, E. J. J. Am. Chem. Soc. 2008, 130, 2954. (d) Prévost, M.; Woerpel, K. A. J. Am. Chem. Soc. 2009, 131, 14182. (9) Raushel, J.; Fokin, V. V. Org. Lett. 2010, 12, 4952. (10) Davies, H. M. L.; Alford, J. S. Chem. Soc. Rev. 2014, 43, 5151 and references therein. (11) Chuprakov, S.; Kwok, S. W.; Zhang, L.; Lercher, L.; Fokin, V. V. J. Am. Chem. Soc. 2009, 131, 18034. (12) Matsuda, T.; Tsuboi, T.; Murakami, M. J. Am. Chem. Soc. 2007, 129, 12596. (13) For a review: (a) D’yakonov, V. A.; Trapeznikova, O. A.; de Meijere, A.; Dzhemilev, U. M. Chem. Rev. 2014, 114, 5775. For recent examples: (b) Charette, A. B.; Jolicoeur, E.; Bydlinski, G. A. S. Org. Lett. 2001, 3, 3293. (c) Yashin, N. V.; Averina, E. B.; Grishin, Y. K.; Kuznetsova, T. S.; Zefirov, N. S. Synthesis 2006, 279. (14) A singular example of related intramolecular cyclopropanation of a methylenecyclopropane moiety is reported: Chen, K.; Zhu, Z.-Z.; Zhang, Y.-S.; Tang, X.-Y.; Shi, M. Angew. Chem. Int. Ed. 2014, 53, 6645. (15) Arora, S.; Binger, P. Synthesis 1974, 801. (16) For a review: (a) de Meijere, A.; Kozhushkov, S. I. Chem. Rev. 2000, 100, 93. For selected examples: (b) Gajewski, J. J. J. Am. Chem. Soc. 1970, 92, 3688. (c) Gajewski, J. J.; Burka, L. T. J. Am. Chem. Soc. 1972, 94, 8865. (d) Brinker, U. H.; Wilk, G.; Gomann, K. Angew. Chem. Int. Ed. Engl. 1983, 22, 868. (e) Wiberg, K. B.; Snoonian, J. R. J. Org. Chem. 1998, 63, 1390. (f) Anichini, B.; Goti, A.; Brandi, A.; Kozhushkov, S. I.; de Meijere, A. Chem. Commun. 1997, 261. (17) For reviews: (a) Carpenter, N. E.; Overman, L. E. Org. React. 2005, 66, 1. (b) Majumdar, K. C.; Bhattacharyya, T.; Chattopadhyay, B.; Sinha, B. Synthesis 2009, 2117. For recent examples: (c) Boeckman, R. K.; Genung, N. E.; Chen, K.; Ryder, T. R. Org. Lett. 2010, 12, 1628. (d) Levin, S.; Nani, R. R.; Reisman, S. E. J. Am. Chem. Soc. 2011, 133, 774. (18) Beckhaus, H.-D.; Rüchardt, C.; Kozhushkov, S. I.; Belov, V. N.; Verevkin, S. P.; de Meijere A. J. Am. Chem. Soc. 1995, 117, 11854. (19) Tomooka, K.; Shimada, M.; Uehara, K.; Ito, M. Organometallics 2010, 29, 6632. (20) The absolute configurations of other products were assigned by analogy. (21) Jones, A. C.; May, J. A.; Sarpong, R.; Stoltz, B. M. Angew. Chem. Int. Ed. 2014, 53, 2556. (22) Cope, A. C.; Banholzer, K.; Keller, H.; Pawson, B. A.; Whang, J. J.; Winkler, H. J. S. J. Am. Chem. Soc. 1965, 87, 3644. (23) A further study for the formation of 11 with racemization is under way. (24) For a possible mechanism of isomerization from 9 to 10, see reference 2.
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TOC Graphic: R
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cat. RhII
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cycloasymmetric addition cyclopropanation
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